Metal halide or high pressure sodium

By
Ed Rosenthal
on January 9, 2002

I understand that high pressure sodium and metal halide lamps each offer a different spectrum of light, one towards red and the other towards blue. Which spectrum comes from which bulb, and which bulb is more beneficial for vegetative growth and flowering growth respectively?
“Gotta know to grow!”
Cambridge, Ontario

Both metal halide (MH) and high pressure sodium (HPS) lamps emit most of their light in spectrums which the plants use very inefficiently, yellow and green. Overall, HPS lamps emit more red and blue light, the spectrums that the plants use most efficiently to fuel photosynthesis. Part of the reason for this is that HPS lamps emit 10-20% more total light.

Vegetative plants grown under 1000 watt HPS lamps grow faster than those under 1000 watt MH lamps. There is absolutely no reason to use MH lamps either in flowering or vegetative growth stages. MH lamps are useful for displaying plants.

If you set up alternating rows of MH and HPS lamps you would notice a wave pattern, with more growth under the HPS lamps.

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